Preforms are well known in the art. Preforms are typically injection molded. In a later operation the preform is blow molded to the final shape, often with the assistance of a stretch rod.
Preforms may be nested, so that an inner preform is disposed within an outer preform. This arrangement provides the benefit that both preforms may be blow molded at the same time and in a single operation. A separate operation to insert one preform inside another is necessary.
But the two, or more, preforms are injection molded in separate operations, requiring assembly to nest the preforms for the single blow molding operation. But assembly, in order to nest the preforms, may occur at a first location. The nested preforms may be shipped to a second location, miles away, for warehousing or blow molding. If warehoused, the nested preforms may be subjected to thermal cycling, and likely shipped again for blow molding. In preparation for the blow molding operation, the nested preforms may be run through a tumbler, bulk sorter and/or stacker.
But the shipping, warehousing, tumbling, sorting and/or stacking operations may dislodge and separate the previously nested preforms. If the preforms become separated, re-assembly is necessary, defeating the purpose of nesting. Previous attempts include: 2012/0132607, U.S. Pat. Nos. 6,499,311, 6,649,121, 8,851,322 and 9,162,372. An aerosol container having a bag therein may be made from a dual layer preform, having plural layers disposed one inside the other. Relevant attempts in the art include U.S. Pat. Nos. 3,450,254; 4,330,066; 6,254,820; RE 30093 E; WO 9108099 and US 2011/0248035 A1.
But some of these attempts rely upon blow molding the nested inner and outer preforms into an inner bag and outer container, respectively. A volume is defined between the inner bag and outer container. The volume must be charged with propellant, then sealed, for future use. But the propellant charge is a separate operation which typically occurs after blowmolding.
Blowmolding typically requires two steps, a low pressure step followed by a high pressure step. The two steps of the operation increase time, and thus cost, of the manufacturing process. And the equipment used in the high pressure blowmolding step must be capable of supplying air at 2700 to 3500 kPa. Such an equipment requirement also adds to manufacturing cost.
After blowmolding, the propellant charge occurs. But the propellant charge requires specialized equipment. This equipment may not be conveniently located adjacent with the product fill, requiring further steps or transport between propellant charge and product fill. Furthermore, if rapid production turnaround is needed, it is advantageous to have fewer steps to be completed when the nested preforms are pulled from inventory.
Accordingly this invention is directed to the problem of reducing post-blowmolding manufacturing steps for making bag-in-bottle plastic aerosol containers using nested preforms.